The present invention relates to a vacuum treatment apparatus and a cleaning method therefor.
In a semiconductor device manufacturing process, semiconductor wafers are subjected to various treatments, such as CVD, etching, ashing, etc., using treatment gases in a vacuum. In carrying out these vacuum treatments, reaction products resulting from reaction between components in the treatment gases or between the treatment gas components and the components of the wafer surface adhere to the susceptors of the wafers and the wall portion of a treatment chamber. Since these adhering products would form a source of particles, they should be removed.
Conventionally, as is described in Jpn. Pat. Appln. KOKAI Publication No. 4-56770, for example, a cleaning gas is introduced into the treatment chamber after plasma CVD is carried out by using a parallel-plate CVD apparatus. At the same time, voltage is applied between electrodes to convert the gas into a plasma. The interior of the treatment chamber is cleaned with use of the plasma.
According to this method, however, the region where the plasma is generated is limited, so that the adhering products cannot be thoroughly removed from the side faces of the susceptors and the base and corner portions of the treatment chamber. Moreover, this method is not applicable to an apparatus in which the treatment gases are caused to react without using electrical energy.
In filling contact holes of MOS transistors, for example, TiN (titanium nitride) films for use as barrier layers are interposed between aluminum and tungsten layers and diffusion layers. TiCl.sub.4 gas and NH.sub.3 gas are fed into the treatment chamber, and the wafers are heated to, for example, 500.degree. C. to 750.degree. C. TiN is formed as TiCl.sub.4 and NH.sub.3 are caused to react by the resulting heat. In this case, NH.sub.4 Cl (ammonium chloride) is formed as a reaction by-product besides TiN. Since NH.sub.4 Cl solidifies at a temperature of about 120.degree. C. or below, and in a substantially decompressed vacuum, it adheres to the inner wall surfaces of the treatment chamber and pipes at 120.degree. C. or below. The adhering NH.sub.4 Cl powders and scatters during evacuation, thus lowering the degree of vacuum and contaminating the wafers.
Since the TiN films are formed by thermal CVD, as mentioned before, plasma cleaning requires additional electrodes. For the aforesaid reason, however, NH.sub.4 Cl cannot be thoroughly removed even with use of those additional electrodes. Accordingly, the treatment chamber is drained periodically. According to this method, however, the corner portions cannot be cleaned satisfactorily.
If the build-up at the corner portions of the treatment chamber increases, therefore, the apparatus must be disassembled to be cleaned. More specifically, the top plate or the like of the treatment chamber is removed to expose its interior to the atmosphere, and various components are detached. Then, an operator directly wipes the inner wall surface and the like of the treatment chamber with a wiper soaked with a cleaning agent, such as pure water. After this wiping operation is finished, the treatment chamber is evacuated. When a predetermined degree of vacuum is attained, films can be formed again.
Since sputtering requires a degree of vacuum of about 10.sup.-8 Torr, however, each cycle of evacuation takes a whole day and night. On the other hand, the CVD requires a degree of vacuum of about 10.sup.-4 Torr, so that each cycle of evacuation takes about half a day, that is, the downtime is very long. Moreover, the reaction products deposited at the corner portions of the treatment chamber cannot be removed by the wiping operation, and they form a source of polluted particles, thereby lowering the yield of production of devices. Conventionally, therefore, the wiping operation should be combined with periodical overhauling, including operations for disassembling, cleaning, and assembling the whole treatment chamber. In some cases, this overhauling requires several days, so that the downtime is very long. Thus, there has conventionally been a demand for the improvement of the operating efficiency.